JP5457357B2 - Data transmission / reception method using phase transition based precoding and transmitter / receiver supporting the method - Google Patents

Description

  The present invention relates to a generalized or extended phase transition-based precoding method in a multi-input multi-output (MIMO) system using a plurality of subcarriers, and a transceiver supporting the same. And a data transmission / reception method using precoding.

  In recent years, with the universalization of information communication services, the appearance of various multimedia services, and the appearance of high quality services, the demand for wireless communication services has increased rapidly. In order to cope with this actively, an increase in the capacity of the communication system is particularly required.

  As a method for increasing the communication capacity in a wireless communication environment, a method of newly finding an available frequency band and a method of increasing the efficiency for limited resources are conceivable. In particular, for the latter method, a transmitter / receiver is equipped with multiple antennas to obtain diversity gain by further securing a space area for resource utilization, or by transmitting data in parallel through each antenna. Recently, so-called MIMO transmission / reception technology for increasing capacity has attracted much attention and is being actively developed.

  Among such MIMO transmission / reception techniques, in particular, a general structure of a multi-input multi-output (MIMO) system based on orthogonal frequency division multiplexing (OFDM) is shown in FIG. This is described as follows.

  FIG. 1 is a block diagram of an orthogonal frequency division multiplexing system having multiple transmission / reception antennas.

  Referring to FIG. 1, at the transmission end, the channel encoder 101 adds redundant bits to the transmission data bits to reduce the influence of the channel and noise, and the mapper 103 converts the data bit information into data symbol information, The parallel (S / P) converter 105 parallelizes the data symbols so as to be carried on a plurality of subcarriers, and the MIMO encoder 107 converts the parallelized data symbols into a space-time signal.

  At the receiving end, the MIMO decoder 109, the parallel-serial (P / S) converter 111, the demapper 113, and the channel decoder 115 are the reverse functions of the MIMO encoder 107, the serial-parallel converter 105, the mapper 103, and the channel encoder 101 at the transmitting end. Do each.

  In the MIMO OFDM system, various techniques for increasing the transmission reliability of data are required, and in particular, a space-time code (STC) and a cyclic delay are used as a scheme for increasing the space diversity gain. There are diversity (Cyclic Delay Diversity; CDD) and the like, and methods for increasing the signal-to-noise ratio (SNR) include beamforming (BF), precoding, and the like. Here, space-time code and cyclic delay diversity are mainly used to increase transmission reliability of an open loop system in which feedback information is not available at the transmitting end, and beamforming and precoding are used to improve feedback information at the transmitting end. It is used to maximize the signal-to-noise ratio through relevant feedback information in available closed loop systems.

  Among the above methods, cyclic delay diversity and precoding will be described in particular as a method for increasing the spatial diversity gain and a method for increasing the signal-to-noise ratio.

  The cyclic delay diversity technique is a system having a plurality of transmission antennas. When transmitting an OFDM signal, all antennas transmit signals with different delays or different sizes, thereby increasing frequency diversity gain at the receiving end. How to get.

  FIG. 2 is a diagram illustrating a transmission end configuration of a MIMO system using a cyclic delay diversity technique.

  Referring to FIG. 2, an OFDM symbol is transmitted to each antenna through a serial-to-parallel converter and a MIMO encoder, and then a cyclic prefix (CP) for preventing inter-channel interference is added to the receiving end. Is transmitted. At this time, the data sequence transmitted to the first antenna is transmitted to the receiving end as it is, but the data sequence transmitted to the next antenna is cyclically delayed by a certain number of samples compared to the previous antenna and transmitted. .

  On the other hand, when such a cyclic delay diversity technique is implemented in the frequency domain, the cyclic delay can be expressed by a product of phase sequences. Next, the details will be described with reference to FIG.

  FIG. 3 is a configuration diagram of a transmission end of a MIMO system using a conventional phase transition diversity technique (PSD).

  That is, as shown in FIG. 3, after multiplying each data sequence in the frequency domain by a predetermined phase sequence (phase sequence 1 to phase sequence M) set for each antenna, fast inverse Fourier transform (IFFT) was performed. Although it can be transmitted later to the receiving end, this is referred to as a phase shift diversity (PSD) technique.

  With phase transition diversity technique, a flat fading channel can be changed to a frequency selective channel to obtain frequency diversity gain through channel coding or multi-user diversity gain through frequency selective scheduling be able to.

  On the other hand, the precoding scheme includes a codebook based precoding scheme used when the feedback information is finite in a closed loop system, and the channel information is quantized to provide feedback. There is a method to do. In particular, codebook-based precoding is a method of obtaining a signal-to-noise ratio (SNR) gain by feeding back an index of a precoding matrix already known at a transmission / reception end to the transmission end.

  FIG. 4 is a diagram illustrating a configuration of a transmission / reception end of the MIMO system using the above-described codebook-based precoding.

Referring to FIG. 4, the transmitting end and the receiving end each have a finite precoding matrix (P1 to PL), and the receiving end uses the channel information to set the optimum precoding matrix index (l) at the transmitting end. At the transmitting end, the precoding matrix corresponding to the fed back index is applied to the transmission data (χ _{1 to} χ _Mt ). For reference, Table 1 below shows an example of a codebook that can be applied when using 3-bit feedback information in an IEEE 802.16e system having two transmit antennas and supporting a spatial multiplexing rate of 2. Represents.

  In addition to the advantages described above, the phase transition diversity method described above is currently attracting a great deal of attention because it can obtain a frequency selective diversity gain in an open loop and a frequency scheduling gain in a closed loop. However, since the spatial multiplexing rate is 1, a high data transmission rate cannot be expected, and there is a problem that it is difficult to obtain the above gain when resource allocation is performed in a fixed manner.

  In addition, the above-described codebook-based precoding method has an advantage in that effective data transmission is possible because a high spatial multiplexing rate can be used without requiring a small amount of feedback information (index information). Since a stable channel must be secured for feedback, it is unsuitable for a mobile environment where channel changes are severe, and is particularly applicable only in a closed loop system.

  Accordingly, the present invention is directed to a phase transition based precoding method for substantially solving the limitations and problems of the prior art described above and a transceiver supporting the same.

  The object of the present invention is to solve the above-mentioned problems of the phase transition diversity scheme and the precoding scheme, in various manners by phase transition based precoding method and generalization or extension of the phase transition based precoding matrix. It is to provide a method of applying a base precoding scheme.

  Additional advantages, objects, and features of the present invention will become apparent to those skilled in the art from the following description. The objectives and other advantages of the invention may be realized by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

  One aspect of the present invention for achieving the above object is a data transmission / reception method in a multi-input multi-output (MIMO) system using a plurality of subcarriers, which is a part of a phase transition-based precoding matrix. Determining a precoding matrix; determining a first diagonal matrix for phase transition as part of the phase transition based precoding matrix; and unitary matrix as part of the phase transition based precoding matrix. Determining and multiplying a product of a precoding matrix, a diagonal matrix, and a unitary matrix by a symbol of a corresponding subcarrier to perform precoding.

  Another aspect of the present invention is a transceiver that performs data transmission in a MIMO system using a plurality of subcarriers, determines a precoding matrix as part of a phase transition based precoding matrix, and performs phase transition based precoding. After determining a first diagonal matrix for phase transition as part of the coding matrix and determining a unitary matrix as part of the phase transition based precoding matrix, the precoding matrix, diagonal matrix and unitary matrix are A precoding matrix determination module that multiplies and determines a phase transition-based precoding matrix; and a precoding module that performs precoding by multiplying the determined phase transition-based precoding matrix by a symbol of a corresponding subcarrier. Can be included.

  In these aspects, the precoding matrix may be selected by cyclically repeating a precoding matrix in the first codebook with a predetermined period based on a subcarrier index or a frequency resource index, It may be selected by performing a modulo operation of the codebook size on the subcarrier index or frequency resource index. At this time, the precoding matrix is included in the first codebook and is selected only from a precoding matrix including at least one of 1, -1, j, and -j as an element, or the first code It may be selected from a second codebook that is included in the book and is composed of only one or a plurality of precoding matrices including at least one of 1, -1, j, and -j as elements.

  Still another aspect of the present invention is a data transmission / reception method in a MIMO system using a plurality of subcarriers, the step of determining a precoding matrix, and the step of performing precoding on a corresponding subcarrier or virtual resource. The precoding matrix is data that cyclically repeats and selects a plurality of precoding matrices in the first codebook at a predetermined period based on the index “k” of the corresponding subcarrier or virtual resource. Provide a transmission / reception method.

  The foregoing general description of the invention and the following detailed description are exemplary and are intended to provide additional explanation to the claimed invention.

  According to the present invention, efficient communication can be enabled by using a phase transition-based precoding scheme that complements the disadvantages of conventional cyclic delay diversity, phase transition diversity, and precoding scheme, By generalizing or extending the transition-based precoding technique, it is possible to simplify the design of the transceiver and further improve the communication efficiency.

It is a block block diagram of the orthogonal frequency division multiplexing system which has multiple transmission / reception antennas. It is a block diagram of the transmission end of a MIMO system using a conventional cyclic delay diversity technique. It is a block diagram of the transmission end of a MIMO system using a conventional phase transition diversity technique. It is a block diagram of a transmission / reception end of a MIMO system using a conventional precoding technique. It is a block diagram which shows the main structures of the transmitter / receiver for performing the phase transition based precoding. It is a graph which shows two types of application examples of phase transition based precoding or phase transition diversity. 1 is a block diagram illustrating an example of a configuration of an SCW OFDM transmitter to which a phase transition based precoding technique is applied according to the present invention. FIG. FIG. 2 is a block diagram illustrating a configuration of an MCW OFDM transmitter according to the present invention.

  The accompanying drawings are included to provide a better understanding of the invention and illustrate embodiments of the invention and together with the description serve to explain the spirit of the invention.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, throughout the present specification, the same components will be described using the same reference numerals in common.

  Prior to describing the present invention, the terminology used in the present invention was selected from general terms that are widely used as much as possible. However, in some cases, some terms were arbitrarily selected by the applicant. In that case, since the meaning is described in detail in the explanation section of the corresponding invention, it is clarified that the present invention must be grasped not as a simple term name but as a meaning of the term. I want.

  For convenience of explanation and understanding of the present invention, well-known structures and devices are omitted as appropriate, or shown in a block diagram or flowchart form. In the drawings, the same components are denoted by the same reference numerals as much as possible.

<Example 1>
Phase Transition Based Precoding Matrix FIG. 5 is a block diagram showing the main configuration of a transceiver for performing phase transition based precoding.

  Phase transition-based precoding is a method of multiplying all streams to be transmitted with sequences having different phases and transmitting the multiplied streams through all antennas. In general, when a phase sequence is generated using a small cyclic delay value, the channel size may increase or decrease depending on the frequency domain while causing frequency selectivity in the channel from the viewpoint of the receiver.

  As shown in FIG. 5, the transmitter allocates a user terminal to a portion of a frequency band that fluctuates due to a relatively small cyclic delay value so that the frequency is increased and the channel state is good, thereby providing a scheduling gain. Secure. At this time, the transmitter uses a phase transition based precoding matrix to apply a cyclic delay value that increases or decreases constantly for each antenna.

  The phase transition-based precoding matrix P can be expressed by Equation 1 below.

[Formula 1]

（ｉ＝１，…，Ｎ_t、ｊ＝１，…，Ｒ）は、ｋにより決定される複素重みを表す。また、Ｎ_tは、送信アンテナの個数を表し、Ｒは、空間多重化率を表す。 Here, k represents an index of a subcarrier or an index of a specific frequency band,

(I = 1,..., N _t , j = 1,..., R) represents a complex weight determined by k. N _t represents the number of transmission antennas, and R represents the spatial multiplexing rate.

  Here, the complex weight may have different values depending on the OFDM symbol multiplied by the antenna and the index of the corresponding subcarrier. The complex weight may be determined according to at least one of channel status and presence / absence of feedback information.

  On the other hand, the precoding matrix P of Equation 1 is preferably a unitary matrix in order to reduce channel capacity loss in the MIMO system. Here, the channel capacity of the MIMO open loop system can be expressed by an equation in order to examine the configuration conditions of the unitary matrix.

[Formula 2]

Here, H represents a MIMO channel matrix having a size of (N _r × N _t ), and N _r represents the number of receiving antennas. When the phase transition-based precoding matrix P is applied to the above Equation 2, it is as follows.

[Formula 3]

As can be seen from Equation 3, in order to prevent loss of channel capacity, it must be the PP ^H is the identity matrix (Identity Matrix), thus, the precoding matrix P of the phase shift-based, such as the following The condition must be met.

[Formula 4]

  In order for the phase transition-based precoding matrix P to become a unitary matrix, the following two conditions, that is, the power constraint condition and the orthogonal constraint condition must be satisfied simultaneously. The power constraint condition is that the size of each column forming the matrix is set to 1, and this condition is expressed by the following formula (5).

[Formula 5]

  The orthogonal constraint condition is to give orthogonal characteristics between the columns of the matrix. When this condition is expressed by an expression, it is as shown in the following expression 6.

[Formula 6]

  Next, an example of a generalized expression for a 2 × 2 phase transition-based precoding matrix is presented, and a relational expression for satisfying the above two conditions will be described.

  Expression 7 represents a general expression of a phase transition-based precoding matrix having two transmission antennas and a spatial multiplexing rate of 2.

[Formula 7]

Here, α _i and β _i (i = 1, 2) have real values, θ _i (i = 1, 2, 3, 4) represents a phase value, and k is a subcarrier index of the OFDM signal. Represents. In order to make such a precoding matrix a unitary matrix, the power constraint condition of Equation 8 and the orthogonal constraint condition of Equation 9 must be satisfied.

[Formula 8]

[Formula 9]

  Here, “*” represents a conjugate complex number.

  An example of a 2 × 2 phase transition-based precoding matrix that satisfies all of the above Equations 7 to 9 is as follows.

[Formula 10]

Here, θ ₂ and θ ₃ have a relationship as shown in Expression 11 depending on the orthogonal constraint condition.

[Formula 11]
kθ ₃ = −kθ ₂ + π (11)

The precoding matrix may be stored in the form of a codebook in the memory at the transmitting end and the receiving end, and this codebook contains various precoding matrices generated through a finite number of different θ ₂ values. Can be included.

Here, the θ ₂ value can be set appropriately depending on the channel status and the presence / absence of feedback information. When feedback information is used, θ ₂ is set small, and when feedback information is not used, θ ₂ is increased. A high frequency diversity gain can be obtained by setting.

  Meanwhile, the frequency diversity gain or the frequency scheduling gain can be obtained according to the size of the delay sample applied to the phase transition based precoding.

  FIG. 6 is a graph showing two application examples of phase transition based precoding according to the size of the delay sample.

  As shown in FIG. 6, when a large delay sample (or cyclic delay) is used, the frequency selectivity period is shortened, so that the frequency selectivity is high, and the channel code can eventually obtain a frequency diversity gain. . This is preferably used mainly in an open loop system in which the reliability of feedback information is low due to severe channel change over time.

  In addition, in the case where a small delay sample is used, in the frequency selective channel changed from the flat fading channel, there are a portion where the channel size is increased and a portion where the channel size is decreased. Therefore, the channel size increases in a certain subcarrier region of the OFDM signal, and the channel size decreases in other subcarrier regions.

  In such a case, in an orthogonal frequency division multiple access (OFDMA) system that accommodates a large number of users, when a signal is transmitted through a fixed frequency band in which the channel size is increased for each user, signal-to-noise The ratio (Signal to Noise Ratio; SNR) can be increased. In addition, since the frequency band in which the channel size is increased for each user frequently occurs, a multiuser diversity scheduling gain can be obtained for the system. On the other hand, for the receiving side, it is only necessary to transmit only channel quality indicator (CQI) information of a subcarrier region in which each resource allocation is possible as feedback information, so that the feedback information is relatively reduced. There is also.

  The delay sample (or cyclic delay) for phase transition-based precoding may be a value predetermined by the transmitter / receiver or a value transmitted by the receiver to the transmitter through feedback.

  Similarly, the spatial multiplexing rate R may be a value determined in advance by the transmitter / receiver, but the receiver can periodically grasp the channel state and calculate the spatial multiplexing rate and feed it back to the transmitter. The transmitter can also calculate and change the spatial multiplexing rate using the channel information fed back by the receiver.

<Example 2>
The phase transition-based precoding matrix described above in the generalized phase transition diversity matrix has an antenna number N _t (N _t is a natural number of 2 or more) and a spatial multiplexing rate R (R is a natural number of 1 or more). ) Can be expressed in the form of Equation 12 below.

[Formula 12]

  Equation 12 can be regarded as a generalized representation of the conventional phase transition diversity method. Therefore, in the following, the MIMO method according to Equation 12 is referred to as generalized phase shift diversity (GPSD). Shall be called.

は、Ｎ_t個の送信アンテナとＲの空間多重化率を持つＭＩＭＯ−ＯＦＤＭ信号のｋ番目のサブキャリアに対するＧＰＳＤ行列を表し、

を満たすユニタリ行列（第２行列）であり、各アンテナに対応するサブキャリアシンボル間の干渉を最小化するために用いられる。特に、位相遷移のための対角行列（第１行列）のユニタリ行列特性をそのまま維持させるために

自体もユニタリ行列の条件を満たすことが好ましい。式１２で周波数領域の位相角θ_i、ｉ＝１，…，Ｎ_tは、時間領域の遅延時間τ_i、ｉ=１，…，Ｎ_tと下記のような関係を持つ。 here,

Represents the GPSD matrix for the kth subcarrier of the MIMO-OFDM signal with N _t transmit antennas and R spatial multiplexing rate,

Is a unitary matrix (second matrix) that is used to minimize interference between subcarrier symbols corresponding to each antenna. In particular, in order to maintain the unitary matrix characteristics of the diagonal matrix (first matrix) for phase transition as it is

It is preferable that the condition itself satisfies the unitary matrix condition. Phase angle θ _{i, i} = 1 in the frequency domain by the formula 12, ..., N _t, the delay time tau _i, i = 1 in the time domain, ..., have a relationship such as N _t and below.

[Formula 13]

Here, N _fft represents the number of subcarriers in the OFDM signal.

  This is a modified example of Equation 12, and the GPSD matrix can be obtained by the following method.

[Formula 14]

  When the GPSD matrix is configured by the method of Equation 14, since the symbols of each data stream (or OFDM subcarrier) are shifted by the same phase, there is an advantage that the configuration of the matrix becomes easy. That is, the GPSD matrix of Equation 12 has the same phase row, whereas the GPSD matrix of Equation 14 has the same phase column, so that each subcarrier symbol is shifted by the same phase. That is why. By expanding Equation 14, the GPSD matrix can be obtained by the following method.

[Formula 15]

  According to Expression 15, since the rows and columns of the GPSD matrix have independent phases, more various frequency diversity gains can be obtained.

  As an example of Equations 12, 14, and 15, a GPSD determinant of a system having two transmission antennas and using a 1-bit codebook is expressed as follows.

[Formula 16]

  Since the β value can be easily determined when the α value is determined by Equation 16, it can be realized that information on the α value is determined as appropriate two values, and the information on this is fed back by a codebook index. For example, if the feedback index is 0, it can be promised in advance between the transceivers that α is 0.2, and if the feedback index is 1, α is 0.8.

の一例として信号対雑音比（ＳＮＲ）利得を得るための所定のプリコーディング行列を用いることができ、このようなプリコーディング行列として、ウォルシュアダマール行列（Walsh Hadamard matrix）またはＤＦＴ行列を用いることができる。特に、ウォルシュアダマール行列が用いられた場合の式１２によるＧＰＳＤ行列の一例は、下記の通りである。 Unitary matrix in Equations 12, 14, and 15

As an example, a predetermined precoding matrix for obtaining a signal-to-noise ratio (SNR) gain can be used. As such a precoding matrix, a Walsh Hadamard matrix or a DFT matrix can be used. . In particular, an example of a GPSD matrix according to Equation 12 when a Walsh Hadamard matrix is used is as follows.

[Formula 17]

  Equation 17 assumes a system with four transmit antennas and a spatial multiplexing rate of 4, where a specific transmit antenna is selected by appropriately reconfiguring the second matrix (antenna selection), The spatial multiplexing rate can be adjusted (rank adaptation).

は、送信端及び受信端にコードブックの形態で備えられてもよい。この場合、送信端は、受信端からコードブックのインデックス情報がフィードバックされると、自体の持っているコードブックから該当のインデックスの第２行列を選択した後、上記の式１２、１４、１５のいずれかを用いて位相遷移ベースのプリコーディング行列を構成する。 On the other hand, the unitary matrix of Equations 12, 14, and 15

May be provided in the form of a code book at the transmitting end and the receiving end. In this case, when the index information of the codebook is fed back from the receiving end, the transmitting end selects the second matrix of the corresponding index from the codebook held by itself, and then the above Expressions 12, 14, and 15 Either one is used to construct a phase transition based precoding matrix.

として２×２、４×４のサイズのウォルシュコードを用いた場合のＧＰＳＤ行列の一例は、下記の通りである。 Unitary matrix of equations 12, 14, and 15

An example of the GPSD matrix when using a Walsh code of 2 × 2, 4 × 4 size is as follows.

<Example 3>
The phase angle θ _i and / or the unitary matrix U of the diagonal matrix in the time-variable generalized phase transition diversity equations 12, 14, and 15 of the GPSD matrix can be changed with time. For example, the time-variable GPSD for Expression 12 can be expressed by Expression 18 below.

[Formula 18]

は、特定時間ｔでＮ_t個の送信アンテナとＲの空間多重化率を持つＭＩＭＯ−ＯＦＤＭ信号のｋ番目のサブキャリアに対するＧＰＳＤ行列を表し、

を満たすユニタリ行列（第４行列）であり、各アンテナに対応するサブキャリアシンボル間の干渉を最小化するために用いられる。特に、位相遷移のための対角行列（第３行列）のユニタリ行列特性をそのまま維持させるために

自体もユニタリ行列の条件を満たすことが好ましい。式１８で、位相角θ_i(ｔ)、ｉ=１，…，Ｎ_tと遅延時間τ_i(ｔ)、ｉ=１，…，Ｎ_tには、次のような関係が成立する。 here,

Represents a GPSD matrix for the kth subcarrier of a MIMO-OFDM signal having N _t transmit antennas and a spatial multiplexing rate of R at a specific time t,

Is a unitary matrix (fourth matrix) that is used to minimize interference between subcarrier symbols corresponding to each antenna. In particular, in order to maintain the unitary matrix characteristic of the diagonal matrix (third matrix) for phase transition as it is

It is preferable that the condition itself satisfies the unitary matrix condition. In Expression 18, the following relationship holds between the phase angle θ _i (t), i = 1,..., N _t and the delay time τ _i (t), i = 1 _,.

[Formula 19]

Here, N _fft represents the number of subcarriers in the OFDM signal.

  As can be seen from Equations 18 and 19, the time delay sample value and the unitary matrix may change over time, where the time unit may be an OFDM symbol unit or a constant unit time. Good.

  An example of a GPSD matrix using a 2 × 2 Walsh code as a unitary matrix for obtaining a time variable GPSD is shown in Table 4 below.

  An example of a GPSD matrix using a 4 × 4 Walsh code as a unitary matrix for obtaining a time variable GPSD is shown in Table 5 below.

  In the third embodiment, the time-variable GPSD matrix for Expression 12 is described. However, the present invention is equally applicable to the diagonal matrix and the unitary matrix in Expression 14 and Expression 15. Therefore, in the following embodiment, Expression 12 will be taken up and described, but it is obvious to those having ordinary knowledge in the technical field to which the present invention belongs that Expressions 14 and 15 can be equally extended and applied. .

<Example 4>
The expanded GPSD matrix is constructed by adding a third matrix corresponding to the precoding matrix to the GPSD matrix composed of the diagonal matrix and the unitary matrix in the expanded phase transition diversity embodiment of the generalized example 2. Can do. This can be expressed by Equation 20 below.

[Formula 20]

In the expanded GPSD matrix, a precoding matrix P having a size of N _t × R is added in front of the diagonal matrix as compared with Equation 12, and thus the size of the diagonal matrix is changed to R × R. There is a feature in that.

は、特定周波数帯域または特定サブキャリアシンボルにしたがって別々に設定されてもよく、開ループシステムでは固定行列（fixed matrix）に設定されることが好ましい。このようなプリコーディング行列

の追加により最適化された信号対雑音比（ＳＮＲ）利得を得ることができる。または、送信端及び受信端には、複数のプリコーディング行列Ｐを含むコードブック（codebook）が備えられてもよい。 This additional precoding matrix

May be set separately according to a specific frequency band or a specific subcarrier symbol, and is preferably set to a fixed matrix in an open loop system. Such a precoding matrix

To obtain an optimized signal-to-noise ratio (SNR) gain. Alternatively, the transmitting end and the receiving end may be provided with a codebook including a plurality of precoding matrices P.

  On the other hand, at least one of the precoding matrix P, the diagonal matrix phase angle θ, and the unitary matrix U in the extended GPSD matrix can be changed according to time. Therefore, when the index of the next precoding matrix P is fed back in a predetermined time unit or a predetermined subcarrier unit, a specific precoding matrix P corresponding to this index is selected from a predetermined codebook. Can do.

  The extended GPSD determinant according to this embodiment can be expressed as follows.

[Formula 21]

  As an example of an extended GPSD matrix, the determinant for a MIMO system with 2 and 4 transmit antennas can be shown as Equations 22 and 23 below.

[Formula 22]

[Formula 23]

  In the above equations 22 and 23, the DFT matrix is used as the unitary matrix U. However, the matrix is not necessarily limited to this, and any matrix that satisfies unit conditions such as Walsh Hadamard code can be used.

  Further, as another example of the extended GPSD matrix, a determinant for a MIMO system having four transmission antennas can be expressed by the following Expression 24.

[Formula 24]

In Equation 24, the enhanced GPSD matrix, compared to Equation 12, before the N _t × N _t of the size of the diagonal matrix D1 and N _t × R of the size of the precoding matrix P diagonal matrix D2 Therefore, the size of the diagonal matrix D2 is changed to R × R.

は、特定周波数帯域または特定サブキャリアシンボルにしたがって別々に設定されてもよく、開ループシステムでは固定行列と設定されることが好ましい。このようなプリコーディング行列

の追加により最適化された信号対雑音比（ＳＮＲ）利得を得ることができる。 Precoding matrix added above

May be set separately according to a specific frequency band or a specific subcarrier symbol, and is preferably set as a fixed matrix in an open loop system. Such a precoding matrix

To obtain an optimized signal-to-noise ratio (SNR) gain.

  Alternatively, the transmitting end or the receiving end may be provided with a codebook including a plurality of precoding matrices P.

  In this case, the phase angle can be simultaneously changed to two types in one system through the diagonal matrix D1 and the diagonal matrix D2. For example, when a small value phase transition is applied through the diagonal matrix D1 and a large value phase transition is applied through the diagonal matrix D2, a multiuser diversity scheduling gain can be obtained by the former, and a frequency diversity gain can be obtained by the latter. Can be obtained. In this case, the diagonal matrix D1 system may be used for performance improvement, and the diagonal matrix D2 may be used for the purpose of averaging channels between streams. In addition, a large value phase transition may be applied through the diagonal matrix D1 to increase the frequency diversity gain, and a large value phase transition may be applied through the diagonal matrix D2 to average and use the channels between the streams. it can. Such a gain can be obtained from the structure of Equation 21. At this time, the matrix P of Expression 21 can be used after being transformed in units of subcarriers or frequency resources without using feedback information from the receiver. This modified form can be expressed by Equation 25.

[Formula 25]

は、リソースインデックスｋごとに異なるプリコーディング行列Ｐを使用することによって周波数ダイバーシティ利得を増加させ、対角行列とユニタリ行列Ｕを通じて各ストリーム間でチャネルを平均化して使用する特定の場合を表す。 In Equation 25

Represents a specific case where the frequency diversity gain is increased by using a different precoding matrix P for each resource index k, and the channels are averaged and used between the streams through the diagonal matrix and the unitary matrix U.

と、例えば、６個のプリコーディング行列のうち４個のプリコーディング行列のみを使用するように決定されたコードブック

と、は、下記の式２６で表現することができる。 <Example 5>
Use of codebook subset restriction method For example, when a codebook including N _c precoding matrices is used by applying a codebook subset restriction method using only a certain part of the codebook by a base station or a terminal , N _c precoding matrices must be reduced to N _restrict precoding matrices. Here, the codebook subset restriction technique can be used to reduce multi-cell interference or reduce complexity. Here, the condition of N _restrict ≦ N _c must always be satisfied. For example, assuming that the number of all precoding matrices in the codebook is N _c = 6, the codebook having a total of 6 precoding matrices

And, for example, a codebook determined to use only 4 precoding matrices out of 6 precoding matrices

And can be expressed by Equation 26 below.

[Formula 26]

は、コードブック

のインデックスを再配列した等価なコードブックである。上記の式２６におけるコードブック部分集合制限方法を使用する時、受信複雑度を減らすために、コードブックのうち、プリコーディング行列が｛１，−１，ｊ，−ｊ｝の要素でのみ構成されたプリコーディング行列のみを部分集合として使用することができ、要素の大きさは正規化係数によって異なる値を持つことがある。 In equation 26 above, the code book

The codebook

An equivalent codebook with rearranged indices. When using the codebook subset restriction method in Equation 26 above, in order to reduce reception complexity, the precoding matrix of the codebook is composed of only elements {1, -1, j, -j}. Only the precoding matrix can be used as a subset, and the element size may have different values depending on the normalization coefficient.

<Example 6>
Used cyclically repeated precoding matrix codebook example, if precoding matrix set fits between the transmitter and the receiver are predefined in a particular time, which can be represented by the formula 27.

[Formula 27]

In Equation 27, the set of precoding matrices includes N _c precoding matrices. Equation 27 above can be simplified in the form of Equation 28 below.

[Formula 28]

中のプリコーディング行列を、サブキャリアまたはリソースインデックスによって巡回反復して使用する方法を表す。そして、上の式２８で、

は、データストリームをスクランブルする役割を果たすもので、

は、データストリーム置換行列と呼ぶことができ、式２７に示すように、空間多重化率Ｒによって選択されてもよい。

は、下記の式２９のような簡単な形態でも表現可能である。 That is, Expression 27 and Expression 28 represent a code book.

It represents a method of using the precoding matrix in the medium repeatedly by subcarrier or resource index. And in the above equation 28,

Is responsible for scrambling the data stream,

May be referred to as a data stream permutation matrix, and may be selected by a spatial multiplexing rate R as shown in Equation 27.

Can also be expressed in a simple form as shown in Equation 29 below.

[Formula 29]

は、単位行列を含んでもよい。したがって、データストリームをスクランブルする処理は、スキップすることができる。 As shown in Equation 29,

May include an identity matrix. Therefore, the process of scrambling the data stream can be skipped.

を適用すると、式２８は、下記の式３０で表現することができる。 The method of using the precoding matrix cyclically and repeatedly in the code book described above can also be used in a code book to which the code book restriction method is applied. For example, in Equation 26

Is applied, Expression 28 can be expressed by Expression 30 below.

[Formula 30]

中のプリコーディング行列をサブキャリアまたはリソースインデックスによって巡回反復して使用する方法を表す。 In Equation 30 above, k represents a subcarrier or frequency resource index, and N _restrict = 4. That is, Equation 30 represents a codebook with a limited precoding matrix.

This represents a method of using the precoding matrix in a cyclic iteration by using a subcarrier or a resource index.

<Example 6-1>
The equation 28 used by cyclically repeating the precoding matrix in the codebook in a predetermined unit can also be expressed by the following equation 31 depending on the frequency resource setting.

[Formula 31]

  In Equation 31 above, k can represent a subcarrier index or a virtual resource index. When k is a subcarrier index, Equation 31 shows a form in which the precoding matrix changes for every v subcarriers. And when k is a virtual resource index, Formula 31 shows a form in which the precoding matrix changes for every v virtual resources.

Equation 31 represents a case where the precoding matrix can be changed within the N _c precoding matrices. The v value can be determined using the same value as the spatial multiplexing rate of the precoding matrix. For example, it can be used in the form of v = R.

  Also, when applying the codebook subset restriction method described through Equation 26, it is natural that the precoding matrix can be changed to a predetermined number of subcarriers or virtual resource units as described above. This can be expressed by Equation 32 below.

[Formula 32]

Also in the case of Expression 32, as in Expression 31, the precoding matrix can be changed in units of v depending on the v value. However, the difference is that the precoding matrix is changed within N _restrict (≦ N _c ) precoding matrices.

  On the other hand, when the frequency diversity method is applied by applying the cyclic repetition of the precoding matrix for each specific frequency resource using the codebook subset restriction method of the fifth embodiment, the frequency depends on the number of precoding matrices that are cyclically repeated. Diversity gain changes. Hereinafter, various embodiments of the codebook subset restriction technique will be described.

<Example 5-1>
Codebook subset restriction method by spatial multiplexing rate The subsets can be defined separately according to the spatial multiplexing rate (rank). For example, when the spatial multiplexing rate is low, the number of subsets is increased to obtain the maximum frequency diversity gain, and when the spatial multiplexing rate is high, the number of subsets is decreased while maintaining performance. Complexity can be reduced.

  Expression 33 represents an example of a method for defining codebook subsets having different sizes depending on each spatial multiplexing rate.

[Formula 33]

は空間多重化率Rによるコードブックの部分集合のプリコーディング行列の個数を表す。これにより、実施例５のコードブック部分集合制限手法を適用したコードブックに対してプリコーディング行列を巡回反復して使用する場合、受信機の複雑度を減らし、性能を向上させることができる。 In Equation 33 above,

Represents the number of precoding matrices of a subset of the codebook with spatial multiplexing rate R. As a result, when the precoding matrix is used cyclically and repeatedly for the codebook to which the codebook subset restriction method of the fifth embodiment is applied, the complexity of the receiver can be reduced and the performance can be improved.

<Example 5-2>
Codebook Subset Limiting Technique with Channel Coding Rate Subsets can be defined separately according to channel coding rate. For example, the frequency diversity gain can usually obtain high performance when the channel coding rate is low, and may rather degrade when the channel coding rate is high. Therefore, in the same spatial multiplexing rate environment, the performance can be optimized by using codebook subsets having different sizes depending on the channel coding rate.

<Example 5-3>
Codebook subset restriction method by retransmission Different subsets can be defined considering retransmission. For example, the retransmission success probability of the receiver can be increased by using a subset other than the codebook subset used at the time of the initial transmission. Therefore, by using the cyclic repetition method of the precoding matrix with different subsets, although the number of precoding matrices of the codebook subset is the same, depending on whether it is a retransmission or the number of retransmissions, System performance can be improved.

<Example 7>
By using power values of different magnitude depending on frequency or time for each transmission antenna, it is possible to improve performance or use power efficiently for the generalized phase transition diversity extended precoding method using power control for each transmission antenna. Can be.

  For example, the power control method for each transmission antenna can be applied using Equation 28, Equation 30, Equation 31, and Equation 32. In particular, application examples of Formula 31 and Formula 32 to the embodiment can be expressed by Formula 34 and Formula 35 below.

[Formula 34]

は、上述のように、データストリームをスクランブルする役割を果たすもので、式２９のような形態でも表現可能である。そして、

は、対角行列であり、ｍ番目の周波数領域またはｔ時間によって各送信アンテナ別に異なる大きさの電力を伝送できるようにする電力制御対角行列を表す。また、

は、ｉ番目の送信アンテナのｍ番目の周波数領域でｔ時間に用いられる電力制御係数を表す。 In Equation 34 above,

As described above, plays a role of scrambling the data stream, and can be expressed in the form of Equation 29. And

Is a diagonal matrix, which represents a power control diagonal matrix that enables transmission of different magnitudes of power for each transmit antenna depending on the mth frequency region or t time. Also,

Represents a power control coefficient used at time t in the m-th frequency region of the i-th transmission antenna.

Equation 34 above expresses a scheme in which power control for each transmission antenna is applied to a scheme using cyclic repetition using a codebook having N _c precoding matrices, and Equation 35 below represents Equation 32. The codebook subset restriction method is used to express a scheme in which cyclic antenna power control is applied to a scheme using cyclic iteration.

[Formula 35]

のそれぞれは、上記の式３４におけるのと同様のものを表す。ただし、プリコーディング行列がＮ_restrict（≦Ｎ_c）個のプリコーディング行列内で巡回反復されるという点が異なる。 Even in Equation 35,

Each represents the same as in Equation 34 above. However, the difference is that the precoding matrix is cyclically repeated within N _restrict (≦ N _c ) precoding matrices.

<Example 8>
Transceivers that perform phase transition based precoding Generally, a communication system includes a transmitter and a receiver. Here, the transmitter and the receiver may be a transceiver that performs both the transmission function and the reception function. However, in order to clarify the explanation regarding feedback, usually, one of the persons in charge of data transmission is a transmitter and the other of the transmitters that transmits feedback data is a receiver.

  On the downlink, the transmitter may be part of the base station and the receiver may be part of the terminal. On the uplink, the transmitter may be part of the terminal and the receiver may be part of the base station. The base station can include a plurality of receivers and a plurality of transmitters, and the terminal can also include a plurality of receivers and a plurality of transmitters. In general, each configuration of the receiver performs an inverse function of each configuration of the corresponding transmitter, and therefore only the transmitter will be described in detail below.

  FIG. 7 is a block diagram showing a configuration of an embodiment of an SCW OFDM transmitter to which a phase transition based precoding technique is applied, and FIG. 8 is a block diagram showing a configuration of an embodiment of an MCW OFDM transmitter. It is.

  Referring to FIGS. 7 and 8, channel encoders 510 and 610, interleavers 520 and 620, fast inverse Fourier transformers (IFFT) 550 and 650, analog converters 560 and 660, and other configurations are those shown in FIG. Therefore, the detailed description thereof will be omitted, and only the precoders 540 and 640 will be described in detail here.

  The precoders 540 and 640 include precoding matrix determination modules 541 and 641 and precoding modules 542 and 642, respectively.

  The precoding matrix determination modules 541 and 641 determine the phase transition-based precoding matrix in any one of the first group of equations 12, 14, and 15 and the second group of equations 20 and 21. Since the specific precoding matrix determination method has been described in detail through the second to fourth embodiments, the details thereof are omitted here. The phase transition-based precoding matrix determined in one form of the first group of equations 12, 14, 15 and the second group of equations 20, 21 is a subcarrier according to time as represented by equation 18. The precoding matrix for eliminating inter-interference, the phase angle of the diagonal matrix and / or the unitary matrix can be changed.

  Also, the precoding matrix determination modules 541 and 641 can select at least one of the precoding matrix and the unitary matrix based on information fed back from the receiving end. At this time, the feedback information is a matrix for a predetermined codebook. It is preferable to include an index.

  The precoding modules 542 and 642 perform precoding by multiplying the determined subcarrier of the OFDM symbol by the determined phase transition based precoding matrix.

  The reception process of the MIMO-OFDM system using the phase transition based precoding is performed in the reverse process of the transmission process described above. The process is briefly described as follows. First, MIMO channel information for a corresponding subcarrier in which data is transmitted is obtained using pilot symbols for channel estimation, and an equivalent channel is obtained by multiplying the channel information by the determined phase transition-based precoding matrix. get information. Using the equivalent channel information and the received signal vector obtained in this way, a signal transmitted by being precoded on a phase transition basis through various MIMO receivers is extracted. The data signal thus extracted is subjected to error correction through channel decoding, and finally transmission data information is obtained. This process may be repeated depending on the MIMO reception technique, and may include additional decoding processes. Since the phase transition based precoding method used in the present invention is not modified by the MIMO reception method, a detailed MIMO reception method will not be described.

  It should be noted that most of the terms disclosed in the present invention are defined in view of the function of the present invention and may differ from the intent or ordinary usage of those skilled in the art. Therefore, it is desirable that the above terms are understood based on all the contents disclosed in the present invention.

  Although the present invention has been described above with reference to specific embodiments, those having ordinary knowledge in the technical field to which the present invention pertains have various variations within the scope that does not depart from the technical idea and essential features of the present invention. It is clear that various modifications can be made. Accordingly, the embodiments described above are illustrative in all aspects and should not be construed as limiting. The scope of the present invention is not limited to the above detailed description, but is defined by the appended claims, and any modified or modified embodiments derived from the claims and equivalents thereof are within the scope of the present invention. include.

  As is apparent from the above, according to the present invention, efficient communication is enabled through a phase transition based precoding technique that overcomes the drawbacks of the conventional cyclic delay diversity, phase transition diversity and precoding techniques, By generalizing or extending the phase transition-based precoding technique, it is possible to simplify the design of the transceiver and improve the communication efficiency.

  The above description of the preferred embodiments of the present invention is exemplary, and those skilled in the art can make various modifications, additions, and alternatives without departing from the characteristics of the present invention.

Claims (20)

A method of transmitting a signal by a transmitter of a MIMO system using a plurality of antennas, comprising:
Encoding the encoder input signal and outputting multiple streams;
Precoding the plurality of streams using a specific precoding matrix selected from a first codebook by a precoder and mapping to the plurality of antennas;
Transmitting signals mapped to the plurality of antennas to a receiver;
Including
The first codebook includes N _restrict precoding matrices, each of the N _restrict precoding matrices having an index i, i = 0, 1,..., N _restrict −1, The specific precoding matrix is selected by i = s mod N _restrict , where “mod” represents a modulo operation, s is a variable that changes every v consecutive subcarriers, and v is A predetermined integer,
The first codebook is a subset of a second codebook;
The second codebook has N _c precoding matrices, where N _c > N _restrict ,
The first codebook includes two or more precoding matrices having one or more matrix elements selected only from the group consisting of “1”, “−1”, “j”, and “−j”. Predetermined to have,
The signal transmission method, wherein the second codebook further includes a precoding matrix having matrix elements other than the group composed of the “1”, “−1”, “j”, and “−j”. The s is

And
The k is an index of a subcarrier or a virtual resource, the v is the predetermined integer, and the s is a variable that changes for each of the v consecutive subcarriers. The signal transmission method described. The signal transmission method according to claim 1, wherein the size of the matrix element is based on a normalization coefficient of the two or more precoding matrices.   The signal transmission method according to claim 1, wherein the subset of the second codebook is predetermined according to a rank or a spatial multiplexing rate.   The signal transmission method according to claim 1, wherein the subset of the second codebook is predetermined according to an encoding condition. A transceiver for transmitting signals in a MIMO system using a plurality of antennas,
An encoder that encodes the input signal and outputs multiple streams;
A precoder that precodes the plurality of streams using a specific precoding matrix selected from a first codebook and maps the plurality of streams to the plurality of antennas;
The plurality of antennas for transmitting signals mapped to the plurality of antennas to a receiver;
Including
The first codebook includes N _restrict precoding matrices, each of the N _restrict precoding matrices having an index i, i = 0, 1,..., N _restrict −1; The specific precoding matrix is selected by i = s mod N _restrict , where “mod” represents a modulo operation, the s is a variable that changes every v consecutive subcarriers, and v is , A predetermined integer,
The first codebook is a subset of a second codebook;
The second codebook has N _c precoding matrices, where N _c > N _restrict ,
The first codebook includes two or more precoding matrices having one or more matrix elements selected only from the group consisting of “1”, “−1”, “j”, and “−j”. Predetermined to have,
The transceiver, wherein the second codebook further includes a precoding matrix having a matrix element other than the group composed of the “1”, “−1”, “j”, and “−j”. The s is

And
The k is an index of a subcarrier or a virtual resource, the v is the predetermined integer, and the s is a variable that changes for each of the v consecutive subcarriers. The described transceiver.   The transceiver according to claim 6, wherein the subset of the second codebook is predetermined according to a rank or a spatial multiplexing rate. The transceiver according to claim 6, wherein the size of the matrix element depends on a normalization coefficient of the two or more precoding matrices.   The transceiver according to claim 6, wherein the subset of the second codebook is predetermined according to an encoding condition. A method of receiving a signal by a receiver of a MIMO system using a plurality of antennas, comprising:
Receiving the signal transmitted from a transmitter using a plurality of antennas;
Obtaining a plurality of streams using a specific precoding matrix selected from the first codebook;
Decoding the plurality of streams at a decoder to obtain transmission information;
Including
The first codebook includes N _restrict precoding matrices, each of the N _restrict precoding matrices having an index i, i = 0, 1,..., N _restrict −1; The specific precoding matrix is selected by i = s mod N _restrict , where “mod” represents a modulo operation, the s is a variable that changes every v consecutive subcarriers, and v is , A predetermined integer,
The first codebook is a subset of a second codebook;
The second codebook has N _c precoding matrices, where N _c > N _restrict ,
The first codebook includes two or more precoding matrices having one or more matrix elements selected only from the group consisting of “1”, “−1”, “j”, and “−j”. Predetermined to have,
The signal reception method, wherein the second codebook further includes a precoding matrix having a matrix element other than the group composed of the “1”, “−1”, “j”, and “−j”. The s is

And
The k is an index of a subcarrier or a virtual resource, the v is the predetermined integer, and the s is a variable that changes for each of the v consecutive subcarriers. The signal receiving method as described. The signal reception method according to claim 11, wherein the size of the matrix element is based on a normalization coefficient of the two or more precoding matrices.   The signal reception method according to claim 11, wherein the subset of the second codebook is predetermined according to a rank or a spatial multiplexing rate.   The signal reception method according to claim 11, wherein the subset of the second codebook is predetermined according to an encoding condition. A transceiver for receiving signals in a MIMO system using a plurality of antennas,
A receiving antenna for receiving the signal transmitted from a transmitter using a plurality of transmitting antennas;
A MIMO decoder for acquiring a plurality of streams using a specific precoding matrix selected from the first codebook;
A decoder for decoding the plurality of streams to obtain transmission information;
Including
The first codebook includes N _restrict precoding matrices, each of the N _restrict precoding matrices having an index i, i = 0, 1,..., N _restrict −1; The specific precoding matrix is selected by i = s mod N _restrict , where “mod” represents a modulo operation, the s is a variable that changes every v consecutive subcarriers, and v is , A predetermined integer,
The first codebook is a subset of a second codebook;
The second codebook has N _c precoding matrices, where N _c > N _restrict ,
The first codebook includes two or more precoding matrices having one or more matrix elements selected only from the group consisting of “1”, “−1”, “j”, and “−j”. Predetermined to have,
The transceiver, wherein the second codebook further includes a precoding matrix having a matrix element other than the group composed of the “1”, “−1”, “j”, and “−j”. The s is

And
The k is an index of a subcarrier or a virtual resource, the v is the predetermined integer, and the s is a variable that changes for each of the v consecutive subcarriers. The described transceiver.   The transceiver according to claim 16, wherein the subset of the second codebook is predetermined according to an encoding condition. The transceiver according to claim 16, wherein the size of the matrix element depends on a normalization coefficient of the two or more precoding matrices.   The transceiver according to claim 16, wherein the subset of the second codebook is predetermined according to a rank or a spatial multiplexing rate.

Images